Silver halide multilayer color reversal photograph materials usually comprises three silver halide dyeforming units sensitive to blue, green and red light respectively associated with yellow, magenta and cyan dye-forming couplers. Said color reversal materials can be divided into two groups: those which do not contain couplers which are used with a developer containing a diffusible coupler and those which contain couplers wherein non-diffusible couplers are incorporated in each of the light sensitive layers of the light sensitive material. Said materials additionally contain other non-light sensitive layers, such as intermediate layers, filter layers, antihalation layers and protective layers, thus forming a multilayerd structure.
Said color reversal materials, after imagewise exposure, are first processed with a black-and-white developer which develops a silver image in the negative exposed areas. This is followed by a reversal fogging step, a second overall exposure or a chemical fogging step, and then developed with a chromogenic developer to form a positive color image.
In order to obtain excellent color reproducibility, each dye-forming unit of the multilayer color reversal photographic material should independently perform its function during storage, exposure and development. In addition, it is necessary that each dye-forming unit should have spectral absorption located in an appropriate wavelength region and contain color couplers capable of providing color images having appropriate spectral absorption. However, it is known that color reversal photographic materials which have been so far developed possess various defects related to the difficulty to meet these requirements.
A first defect relating to color reproduction is that light absorption of the dye obtained from the couplers is not confined to a desired region of the spectrum and extends to other regions of shorter and longer wavelength, thus causing a reduced color saturation.
A second defect is that, during the step of development processing, the development in one light-sensitive emulsion layer may cause unwanted coloration in a neighboring light-sensitive emulsion layer intended by definition to record another image. For example, image development of the green sensitive layer may cause formation of cyan dye in the red sensitive layer following the pattern of the magenta image. This defect results from the diffusion of the oxidation products of the color developing agent, which are produced by the development of one light-sensitive layer, into a neighboring light-sensitive layer where they cause an unwanted reaction with the couplers present in this layer.
A third defect is that a sensitizing dye may diffuse from a specific light-sensitive emulsion layer in which is used into an adjacent light-sensitive emulsion layer to sensitize the adjacent layer thus providing unsuitable spectral sensitization distribution.
These defects will cause the so called "color mixing" or "color contamination" because the reaction of imagewise color formation in a specific light-sensitive emulsion layer disadvantageously affects the neighboring light-sensitive emulsion layer whereby the latter loses its aptitude to form independent elementary color images and forms images which overlap its specific color images.
Various means have been described in the art to reduce or eliminate said color mixing or contamination defects.
One method is to provide intermediate or filter layers comprising reducing agents such as hydroquinone or phenol derivatives, a scavenger for the oxidation products of color developing agents, a coupler forming colorless compound, color couplers forming diffusible dyes and diffusion inhibiting agents for sensitizing dyes or couplers, such as fine silver halide grains, colloidal silica, anionic, anphoteric, nonionic or cationic surfactants, cationic hydrophilic synthetic polymers, polymer latexes, and the like. However, these methods are not satisfactory.
Other methods for removing color mixing and improving color reproduction consist in using an element having a color correcting function. One such method uses colored couplers provided with an auto-masking function as described in U.S. Pat. No. 2,449,966, 2,455,170, 2,600,606, and 3,148,062 and GB 1,044,778. However, this method cannot be applied to positive color reversal materials because unexposed areas would be strongly colored.
Another method employs DIR-couplers (Development Inhibitor Releasing couplers) such as those couplers described by Barr, Thirtle and Wittum in Photographic Science and Eng., vol. 13, pp. 74-80 and pp. 214-217 (1969) or in U.S. Pat. No. 3,227,554. Generally, the DIR coupler imagewise releases in the light-sensitive emulsion layer in which it is used a development inhibitor bringing about an intralayer (or intraimage) effect and causing an improvement in graininess and an improvement in sharpness of color image by the edge effect. The DIR couplers also bring about an interlayer (or interimage) effect. The development inhibitor released in a layer migrates into an adjacent light-sensitive layer thus providing a color correction effect (interimage effect). However, the method of obtaining interimage effects in color reversal photographic materials using DIR couplers is not satisfactory: the effect of a development inhibitor during the first black-and-white development results in a lower silver density with the development in the color developer of a higher silver density and dye image density. As a consequence, interimage effects are mainly produced in the high dye-density areas of the positive image, while it is desirable to obtain interimage effects in low dye-density areas.
Methods for improving color reproducibility of color reversal photographic materials are described in U.S. Pat. No. 3,672,898 and 3,728,121 and in EP 108,250 and 228,561.
In particular, U.S. Pat. No. 3,672,898 describes a color reversal photographic element containing yellow, magenta and cyan dye forming units, each unit having a relative log spectral sensitivity distribution such that good color rendition is obtained upon exposure under any of a variety of illuminants, such as sunlight, tungsten or fluorescent sources.
U.S. Pat. No. 3,728,121 describes a color reversal photographic material comprising a correcting layer of a fine grain silver halide emulsion incorporated among the light sensitive layers of the material with the purpose of improving the color reproduction.
EP 108,250 discloses a color reversal photographic material comprising blue-sensitive, green-sensitive and red-sensitive silver halide emulsion layers at least one of which forms a group consisting of two or three emulsion layers differing in photographic sensitivity. The emulsion layer group contains silver in its high sensitivity constituent layer or in a combination of its high sensitivity constituent layer and its intermediate sensitivity constituent layer in such an amount that it comprises 40 to 80% of the total silver amount in the emulsion layer group. The emulsion layer group contains silver iodide in its high sensitivity constituent layer or in combination of its high sensitivity constituent layer and its intermediate sensitivity constituent layer in such a content that a proportion of the iodide to the all halides in the high sensitivity constituent layer or in combination of the high sensitivity constituent layer and the intermediate sensitivity constituent layer is smaller than that in its low sensitivity constituent layer by 0.3 :mole % or more. Improvements in blue, red and green saturations are reported.
EP 228,561 discloses a reversal color photographic material comprising image forming units, at least one unit comprising a first silver halide emulsion layer spectrally sensitized to a given region of the spectrum with which is associated a dye image-forming coupler and a second silver halide emulsion layer spectrally sensitized to a different region of the spectrum than the first layer and containing an interimage effect-forming means such as a DIR coupler, which forms either a colorless compound or a dye which does not substantially take part in the formation of the image. Improved interimage effects are reported by releasing a development inhibitor during the color development in an emulsion layer which does not participate in the formation of the image.
The multiplicity of color correction methods indicates that none of them has been fully satisfactory. This is particularly true for yellow color reproduction. Generally, with respect to the spectrally sensitive region of a blue-sensitive emulsion layer, the inherently sensitive region of the silver halide is normally utilized as it is, but the spectral absorption of the silver halides lies near the ultraviolet region and is not suitable for the spectral characteristics of a yellow dye image thus causing poor yellow image reproducibility. To extenuate this problem, the blue-sensitive emulsion layer is spectrally sensitized to impart thereto an absorption characteristic in a longer wavelength region. Merocyanine spectral sensitizing dyes such as: ##STR1## are used to accomplish the above purpose. However, such dyes excessively extends the spectral sensitivity region of the blue-sensitive layer toward the longer wavelength side, thus affording an unwanted spectral sensitization region to said layer and decreasing yellow color reproducibility.